Apparatus and method for adhesively connecting wires to a suspension arm in a disk drive assembly

ABSTRACT

A head suspension assembly including a load beam having predefined gluing regions for gluing a bundle of wires thereto. For each gluing region, the load beam is partially-etched with the pattern that includes a plurality of grooves. Preferably, the pattern within the gluing region includes a set of parallel grooves. The gluing regions can be formed at very little cost because partial etching can be performed simultaneously etching other features on the load beam. Advantageously, the gluing regions provide enhanced adhesion between the wires and the load beam which reduces the possibility of failure during manufacture, thereby reducing costs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of Ser. No. 08/912,499 filed Aug. 18,1997 now U.S. Pat. No. 5,808,836 which is a continuation of Ser. No.08/520,995 filed Aug. 30, 1995 now abandoned.

The invention is related to the following commonly-assigned patent:

U.S. Pat. No. 5,074,029, Method for Stringing Wire on an Actuator Arm,by Brooks, Jr. et al. issued Dec. 24, 1991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to transducer suspension systems formagnetic recording media, and more particularly to electricalconnections to a transducer head.

2. Description of the Related Art

Direct access storage devices (DASD) such as disk drives storeinformation on concentric tracks of a rotatable magnetic recording disk.A magnetic head or other transducer element is moved from track to trackto read or record the desired information. Typically, the magnetic headis positioned on an air-bearing slider which "flies" off of the surfaceof the disk as the disk rotates. A head suspension assembly connects theslider to a rotary or linear actuator. The head suspension assemblyprovides support for the slider while allowing it to gimbal duringoperation in order to adjust its orientation as appropriate.

The head suspension assembly typically comprises a load beam attached toan actuator arm, a flexible member (known as a flexure) attached to theload beam, and a slider attached to the flexure.

Examples of suspension systems are shown in the following references:

U.S. Pat. No. 5,208,712, issued May 4, 1992; U.S. Pat. No. 5,172,286,issued Dec. 15, 1992; U.S. Pat. No. 5,138,507, issued Aug. 11, 1992;U.S. Pat. No. 5,074,029, issued Dec. 24, 1991; U.S. Pat. No. 5,063,464,issued Nov. 5, 1991; U.S. Pat. No. 5,012,368, issued Apr. 30, 1991; U.S.Pat. No. 5,003,420, issued Mar. 26, 1991; U.S. Pat. No. 5,001,583,issued Mar. 19, 1991; U.S. Pat. No. 4,996,623, issued Feb. 26, 1991;U.S. Pat. No. 4,996,616, issued Feb. 26, 1991; U.S. Pat. No. 4,991,045,issued Feb. 5, 1991; U.S. Pat. No. 4,937,693, issued Jun. 26, 1990; U.S.Pat. No. 4,853,811, issued Aug. 1, 1989; U.S. Pat. No. 4,884,154, issuedNov. 28, 1989; U.S. Pat. No. 4,868,694, issued Sep. 19, 1989; U.S. Pat.No. 4,807,054 issued Feb. 21, 1989; U.S. Pat. No. 4,167,765, issued Sep.11, 1979; U.S. Pat. No. 3,931,641, issued Jan. 6, 1976; European PatentApplication 484,906, published May 13, 1992; European Patent Application442,225, published Aug. 21, 1991; Japanese Patent Application 01-213821,published Aug. 28, 1989; UK Patent Application 2,193,833, published Feb.17, 1988; IBM Technical Disclosure Bulletin Vol. 33, No. 10B, March1991, page 392; IBM Technical Disclosure Bulletin Vol. 32, No. 3A,August 1989, page 175; and IBM Technical Disclosure Bulletin Vol. 31,No. 12, May 1989, page 203.

In order to electrically connect the transducer head with a read/writecontroller for the a disk drive unit, very thin electrical wires are runacross the suspension assembly. One conventional type of suspensionassembly, such as that disclosed in U.S. Pat. No. 5,012,368 to Bosier etal., includes a fine tube through which the wires pass to the transducerhead. Other suspension assemblies, such as disclosed in U.S. Pat. No.5,001,583 to Matsuzaki, are manufactured with the wires embedded in theload beam.

Some suspension assemblies pass the wires directly over the load beam,without using a tube that disadvantageously increases weight and affectsflexing. This type of suspension assembly is disclosed in U.S. Pat. No.5,074,029 to Brooks, Jr. et al, entitled "Method for Stringing Wire onan Actuator Arm." As disclosed therein, the load beam is attached to aplastic tail (which is eventually discarded) and affixed to a toolingassembly. The wires are positioned across the load beam and tensionedusing a tensioning device on the tooling assembly. A series of glue dotsare then applied to adhesively connect the wires to the load beam.Particularly, uv-curable glue is deposited in dots at predeterminedlocations along the tensioned wires, and the glue dots are then exposedto uv light. After the glue has cured, the wires are ultrasonicallybonded to the transducer, cut and formed into a loop, thereby causing atension imbalance at the glue dot closest to the cut. One problem withthis gluing technique is that the glue dot closest to the transducerhead sometimes pulls away from the load beam due to the tensionimbalance, rendering the part unusable. The glue dots are subjected tofurther stress during subsequent cleaning in an ultrasound bath in whichthe part is shaken. Additionally, the water in the bath causes the glueto swell, which can also contribute to failure of the glue dot.Furthermore, the glue dot on the other side (i.e. the glue dot closestto the actuator arm assembly) sometimes pulls away due to unpredictablethermal expansion differences between plastic and metal.

For these and other reasons, a good adhesive bond at the glue dot isessential for efficient and cost effective manufacturing. One proposedsolution could be to use larger glue dots; however, there are severalproblems associated with large glue dots. Glue application can beunpredictable: liquid glue tends to "wick" along the wire and to spreadto unwanted locations rather than remain in the desired location,causing difficulties in quality control. Uncontrolled spreadingincreases the probability that a part will be unusable. Furthermore, alarger glue dot is more susceptible to thermal expansion stresses. And,glue wicking could cause the thin wires to be too stiff and adverselyaffect performance. Additionally, due to requirements for close spacingbetween disks in modem disk drives, the greater height of such a largerglue dot could cause the thickness of the suspension assembly to causedifficulties during merge of the suspension assemblies into the diskstack.

Another proposed solution to the adhesion problem could be to use agreater number of small dots. However, this approach increasesmanufacturing costs by increasing the time it takes to manufacture apart, and therefore is not an acceptable solution. It would be anadvantage to provide a system for predictably and effectively gluing thewires to a load beam using only a few glue dots.

SUMMARY OF THE INVENTION

In accordance with the objectives of this invention as described aboveand to overcome the limitations of the prior art, a head suspensionassembly having predefined gluing regions and a method for gluing wiresto a head suspension assembly, and particularly for gluing wires to aload beam, is provided. Broadly speaking, the load beam is half-etchedwith a pattern that includes a plurality of grooves at the positionwhere the wires are to be glued. Preferably the pattern includes a setof parallel grooves. Advantageously, the pattern can be obtained at verylittle additional cost because etching the grooves can be performedsimultaneously with etching other features on the load beam.

Gluing the wire to the grooved pattern in the gluing region providesbetter adhesion than the previous practice of gluing the wire to asmooth surface. Furthermore, during glue application, the grooves allowthe glue to flow in a more controlled manner, preventing undesirableflowing and wicking of glue beyond the desired gluing region into otherareas. These advantages, and others, result in reduced adhesion failuresduring manufacture at little or no additional cost, and thereby providea cost effective way of manufacturing suspension assemblies.Additionally, the enhanced adhesion reduces the possibility of failureduring operation of the disk drive unit in which it is installed.

The foregoing, together with other objects, features and advantages ofthis invention, will become more apparent when referring to thefollowing specification, claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

For a more complete understanding of this invention, reference is nowmade to the following detailed description of the embodiments asillustrated in the accompanying drawing, wherein:

FIG. 1 is a side view of a disk drive system and a controller unit inblock form;

FIG. 2 is a top view of a disk drive system;

FIG. 3 is a top view of a load beam including gluing regions having setsof parallel grooves for the preferred embodiment;

FIG. 4 is a cross section of the parallel grooves in the load beam shownin FIG. 3, illustrating the depth and width of etching;

FIG. 5 is an enlarged top view of the tip of the load beam of FIG. 3;

FIG. 6 depicts a load beam installed in a plastic tail and a wire bundlecoupled to the tail and pulled across the load beam by a tensioner;

FIG. 7 is an illustration of the load beam, plastic tail, and wires ofFIG. 6, adding the glue dots and a uv source used for curing the gluedots;

FIG. 8 depicts a completed load beam, illustrating the wires after beingcut and coupled to the transducer head;

FIG. 9 is a cross-section of a glue dot shown in FIGS. 7 and 8,illustrating the coupling between the glue dot, the groove, and showingthe wires passing through in cross-section;

FIG. 10 is an alternative configuration of the gluing region, comprisinga series of concentric circular grooves;

FIG. 11 is still another configuration of the gluing region, comprisinga plurality of dimples;

FIG. 12 is another configuration of the gluing region, comprising aplurality of intersecting grooves to form a mesh pattern including aplurality of islands; and

FIG. 13 is a flow chart illustrating a process for manufacturing a headsuspension assembly using gluing regions on the load beam.

FIG. 14 is a flow chart of a process for forming the gluing regions bypartial etching.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is described in a preferred embodiment in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. While this invention isdescribed in terms of the best mode for achieving this invention'sobjectives. It will be appreciated by those skilled in the art thatvariations may be accomplished in view of these teachings withoutdeviating from the spirit or scope of the invention.

FIGS. 1 and 2 show a side and a top view, respectively, of a disk drivesystem designated by the general reference number 110. The disk drivesystem 110 comprises a plurality of stacked magnetic recording disks 112mounted to a spindle 114. The disks 112 may be conventional particulateor thin film recording disks or, in other embodiments, they may berecently proposed liquid bearing disks. The spindle 114 is attached to aspindle motor 116 which rotates the spindle 114 and disks 112. A chassis120 provides a housing for the disk drive system 110. The spindle motor116 and an actuator shaft 130 are attached to the chassis 120. A hubassembly 132 rotates about the actuator shaft 130 and supports aplurality of actuator arms 134. The stack of actuator arms 134 issometimes referred to as a "comb". A rotary voice coil motor 140 isattached to chassis 120 and to a rear portion of the actuator arms 134.

A plurality of head suspension assemblies 150 are attached to theactuator arms 134. A plurality of transducer heads 152 are attachedrespectively to the suspension assemblies 150. The heads 152 are locatedproximate to the disks 112 so that, during operation, they are inelectromagnetic communication with the disks 112 for reading andwriting. The rotary voice coil motor 140 rotates actuator arms 134 aboutthe actuator shaft 130 in order to move the head suspension assemblies150 to the desired radial position on disks 112. The shaft 130, hub 132,arms 134, and motor 140 may be referred to collectively as a rotaryactuator assembly.

A controller unit 160 provides overall control to system 110. Controllerunit 160 typically includes (not shown) a central processing unit (CPU),a memory unit and other digital circuitry, although it should beapparent that these aspects could also be enabled as hardware logic byone skilled in the computer arts. Controller unit 160 is connected to anactuator control/drive unit 166 which in turn is connected to the rotaryvoice coil motor 140. This configuration allows controller 160 tocontrol rotation of the disks 112. A host system 180. Typically acomputer system, is connected to the controller unit 160. The hostsystem 180 may send digital data to the controller 160 to be stored ondisks 112, or it may request that digital data at a specified locationbe read from the disks 112 and sent to the system 180. The basicoperation of DASD units is well known in the art and is described inmore detail in Magnetic Recording Handbook, C. Dennis Mee and Eric D.Daniel, McGraw-Hill Book Company, 1990.

Reference is now made to FIG. 3 which is a top view of a load beam 150in one preferred embodiment. The load beam 150 comprises a base section308 and opening 320 for connection to the actuator arms 134 (FIGS. 1 and2). Any suitable means may be utilized. For example, a support plate(not shown) may be positioned opposite an arm 134 and the base section300 in order to provide a good support for connecting a load beam 150 tothe arm 134. The support plate is preferably made of a rigid materialsuch as stainless steel, and attaches to the arm by a swage connectionthrough opening 320 and into an opening in the arm 134 or an equivalentattachment. The support plate and the load beam 150 may be attachedtogether by a plurality of welds.

The load beam 150 includes, on the end opposite the tabs 300, a tip 310including any suitable means for attaching to a transducer head.Alternatively, the tip 310 may be attached to a flexure which isconnected to a transducer head. The means for attaching a load beam to atransducer head is not essential to the invention, and will not bediscussed in detail

The load beam 150 includes a plurality of holes 320, 322, 324 and 326.These holes, and others illustrated, are formed into the load beam forpurposes including tooling and controlling the flex of the load beam.

The load beam 150 is an elongate member with upper and lower surfaces.The upper surface 327 includes a plurality of gluing regions including afirst gluing region 330 near the tip 310. A second gluing region 332 ispositioned further from the tip 310, a third gluing region 334 and afourth gluing region 336 are positioned even further from the tip 310.In one embodiment, the first and second gluing regions are alwaysutilized, but the third and fourth gluing regions are selectivelyutilized; i.e., either the third gluing region or the further gluingregion is utilized, but not both. Selective utilization is useful toprevent the glue dots in adjacent suspension assemblies on a single loadarm from interfering with each other and causing problems in assembly.Selective utilization is useful in the preferred embodiment, because twosuspension assemblies are positioned between adjacent disks (such asshown in FIG. 1). For certain designs, the gluing regions may beprovided on the lower surface, or both surfaces, of the load beam.

Reference is now made to FIG. 4 which illustrates a cross section of thegrooves of the second gluing region 332. However, it should be apparentthat the cross section also applies to the other gluing regions 330, 334and 336. The grooves illustrated in FIG. 4 include a first groove 400, asecond groove 402, a third groove 404 and a fourth groove 406. Betweenthe first and second groove is a first land portion 410, between thethird and fourth grooves is a second land portion 412 and between thethird and fourth grooves is a third land portion 414. The width of thefirst groove 400 is w_(g), and the width of the first land portion 410adjacent thereto is w_(s). Preferably, the width w_(g) is equal to thatof w_(s) and therefore, in gluing region 332, there is approximately a50/50 distribution between the surface area associated with each grooveand the surface area associated with the adjacent land.

The height of each groove, illustrated as h_(g) , is approximately 50percent of the thickness of the load beam, illustrated as h_(s). Thethickness in one embodiment of a load beam is 0.0635 millimeters and inanother embodiment it may be 0.076 millimeters. It should be understoodthat the above dimensions and relationships are approximate. Due to thenature of the manufacturing process in which etching is utilized, thedimensions on a manufactured part may vary somewhat but still beacceptable. For example, a 60/40 ratio may be acceptable.

FIG. 5 is an enlarged view of the tip section 310 of the load beam 150.The gluing region, illustrated generally at 330 includes a first set ofparallel grooves 500 and a second set of parallel grooves 510. The firstset of grooves aligned in the direction of the wire that will eventuallybe glued to it. The second set 510 is positioned approximatelyperpendicular, and at the end of one side of the first set 500. Thesecond set 510 is positioned adjacent and crosswise to the first set 500so that an obstacle is presented to glue flowing along each of thegrooves in the first set 500. In other words, when the glue dot isapplied to the gluing region 330, the glue will tend to flow along thegrooves 500 in a direction including that towards the second set 510.The second set 510 will act as a stop and prevent further glue flowingbeyond its edges. An advantage of positioning the second set of groovesin this manner is that glue is prevented from flowing into a region(particularly the tip) in which could adversely affect the stiffnesscharacteristics of the wires in the critical tip region 310.

FIG. 6 illustrates a load beam 150 attached to a tail assembly 600 whichis used for purposes including stringing wires. A tail assembly, and amethod of stringing of wires is disclosed in detail in U.S. Pat. No.5,074,029 to Brooks, Jr. et al. entitled "Method for Stringing Wire onan Actuator Arm", which is expressly incorporated by reference herein.To string the wire, the load beam 150 and the attached tail 600 isaffixed to a tooling assembly (not shown). The wire bundle 610 is strungfrom the tail across the load beam 150 to a tensioning device 620. Thewire bundle 610 includes four wires 630. The wires are positioned andtensioned using the tensioning device 620.

As illustrated in FIG. 7, glue dots are used to affix the wire bundle610 to each gluing region. Particularly, a glue dot 700 is used to affixthe wire bundle 610 to the first gluing region 330, a second glue dot710 is used to affix the wire 610 to the second gluing region 332, and athird glue dot 720 is utilized to affix the wire 610 to the third gluingregion 334.

After the glue dots have all been applied, a uv source 740 is energizedin order to cure the uv sensitive glue. Preferably, the glue comprisesEmcast 1728ETG uv curable adhesive available from Electronic Materials,Inc. of Brookfield, Conn. Any other suitable adhesive (uv curable orotherwise) could be utilized.

FIG. 8 illustrates a completed load beam and transducer head assembly inwhich the wire bundle 610 has been cut near the tip section 310. Thewires in the wire bundle 610 have been individually ultrasonicallybonded to the transducer head 152.

FIG. 9 is a cross section of the glue dot 720 affixed to the thirdgluing region 334 in the load beam 150. It can be seen that the glue hasflowed into each groove, thereby providing a good adhesive bond whileholding the wire bundle 610 in position.

FIG. 10 is a diagram illustrating an alternate embodiment of a gluingregion near the tip 310. As illustrated, the gluing region 330 includesa series of concentric circles illustrated at 1000, including a firstcircular groove 1010, a second circular groove 1012 and a third circulargroove 1014. Of course, a greater or lesser number of grooves may beutilized, depending upon design considerations.

FIG. 11 illustrates still another embodiment of a gluing region 330. Asillustrated, a series of dots or "dimples" are formed as illustrated at1100.

Still another embodiment is illustrated at FIG. 12. The gluing region330 therein includes a plurality of grooves intersecting andperpendicular to each, so that a plurality of islands are formedtherein.

The preferred embodiment includes the plurality of parallel groovesillustrated, for example, in FIG. 5. Several design considerations makethat the preferred embodiment: ease of manufacture, structural integrity(at least in one direction) and glue adhesion.

First, the grooved configuration is easy to specify and simple tomanufacture at little additional cost by etching the grooves at the sametime that the load beam is formed by etching. Particularly, using thegrooves, it is relatively easy to obtain a predictable land/groove ratio(see FIG. 4 for discussion defining the land and groove areas). Thegrooves as illustrated in, for example, FIG. 5 are easier to manufactureutilizing the preferred etching process while still maintaining adesired ratio between the groove to land area in the gluing region. Theconcentric circles configuration of FIG. 10, the dimples of FIG. 11, andthe cross-hatched pattern of FIG. 12 all are more difficult tomanufacture reliably. In summary, the grooves are easier to specify andto reliably manufacture.

A second important issue is the structural effect of each gluing region.Each configuration of the gluing region affects structuralcharacteristics. The cross-hatched gluing region of FIG. 12 and theconcentric circles of FIG. 10 are particularly weak in all directionsdue to disruption of the structure along any axis. The grooves arestrong in a direction parallel to the grooves, but are not as strong ina direction perpendicular to the grooves. The dimpled configuration 1100of FIG. 11 is strong in both directions.

A third important consideration is obtaining a proper bond between theglue and the gluing region. It is difficult to obtain a strong bondbetween the glue and the dimpled region 1110 because, it is believed,that the dimples can hold air bubbles that prevent the glue fromcompletely covering the surface area within the dimple. These bubblestherefore undermine adhesion between the glue dot and the gluing region.The grooved configuration, as well as the other configurations, allowthe glue to flow along the grooves, preventing formation of bubbles andpromoting a good adhesive seal between the glue dot and the gluingregion. Therefore, the grooved configuration is preferred for reasonsincluding ease of manufacture, strength in at least one direction, andpromotion of good adhesion.

Reference is now made to FIG. 13 which is a flow chart illustrating amethod for manufacturing a head suspension assembly using gluing regionson the load beam. As illustrated at 300, gluing regions are first formedin the load beam. These gluing regions may be performed by conventionalmeans, or preferably using the partial etching method describedsubsequently with reference to FIG. 14. At 1310, wire is strung acrossthe load beam over the defined gluing regions. One preferred method ofstringing wires is disclosed in detail in U.S. Pat. No. 5,074,029 toBrooks, Jr. et al., discussed previously. At 1320, glue is applied tothe wire at the gluing region. Then, at 1330, the glue is cured toconnect the wire to the gluing region. If the glue is uv curable, as inthe preferred embodiment, then the uv light is applied at this step.

Reference is now made to FIG. 14 to show a flow chart of the preferredmethod of forming the gluing region. The grooves in the gluing regionsare preferably photolithographically etched into the load beam usingconventional techniques such as described in U.S. Pat. No. 5,353,181, toFrater et al. The gluing regions, as well as other features, are formedat the same time that the load beam is etched from a sheet of metal. Inthe etching process, as illustrated beginning at 1400, a sheet of metalfrom which the load beam is to be made is coated with photoresist. Thenat 1410, the photoresist is exposed on one side with a light patterncorresponding to the gluing regions. As illustrated at 1410 and 1420,both sides are illuminated with a light pattern having the desired shapefor the load beam. At 1430, the photoresist is developed and the exposedsections are removed. At 1440, the sheet is then placed in an acid bathfor a period of time sufficient for the acid to etch away one-half ofthe thickness of the sheet from each side. Thus the grooves in thegluing region, which was exposed only on one side, are half-etched to adepth of approximately one-half of the thickness of the material, whilethe load beam, which was exposed on both sides, is completely detachedfrom the remainder of the metal sheet. In the preferred embodiment, thegrooves have a depth approximately 50 percent. Alternately, the groovesmay be made separately to any desired depth. In some embodiments, thegluing region could be formed by conventional processes other thanetching; however, the cost benefits of etching would not be realized.

Other embodiments and modifications of this invention may occur to thoseof ordinary skill in the art in view of these teachings. Therefore, thisinvention is to be limited only by the following claims, which includeall such embodiments and modifications when viewed in conjunction withthe above specification and accompanying drawings.

We claim:
 1. A method for attaching a wire to a load beam in a headsuspension assembly for a disk drive unit, comprising the steps of:a)forming a plurality of grooves that define at least one gluing region onsaid load beam in the head suspension assembly for the disk drive unit;b) positioning said wire so that a portion of said wire is adjacent tosaid at least one gluing region; c) applying glue to said at least onegluing region on the load beam in the head suspension assembly for thedisk drive unit and said wire adjacent thereto; and d) curing said glueto adhesively connect said wire to said gluing region.
 2. The method ofclaim 1 wherein said step of forming a plurality of grooves includesforming a plurality of parallel grooves and at least one gluing regionon the load beam in the head suspension assembly for the disk driveunit.
 3. A method of forming a gluing region on a load beam for a headsuspension assembly for a disk drive unit, comprising the steps of:a)applying photoresist to both sides of a metal sheet; b) exposing a firstside of the metal sheet with a pattern including the outline of the loadbeam and predefined gluing regions; c) exposing a second side of themetal sheet with the outline of the load beam but not the gluingregions; d) developing said photoresist and removing the exposedsections; and e) placing the resulting product from said step d) into anacid bath for a period of time sufficient to actuate approximatelyone-half of the thickness of the metal sheet.